[osg-users] bounding box of culled geometry

[OpenSceneGraph Users]

Hi Renzo,
Maybe a node visitor with z-near and z-far as parameter is a possible approach.
Werner

On 15. Oktober 2020 09:46:57 MESZ, OpenSceneGraph Users <osg-users at lists.openscenegraph.org> wrote:
>
>Hi Robert,
>
>On 14-Oct-20 3:56 PM, OpenSceneGraph Users wrote:
>
>Hi Renzo,
>
>
>On Wed, 14 Oct 2020 at 12:00, OpenSceneGraph Users
><osg-users at lists.openscenegraph.org> wrote:
>
>I am using osg::Drawable::getBoundingBox() to retrieve the bounding box
>around the whole geometry. Is there a similar short way to get the
>equivalent box for just the culled geometry or do I need to write my
>own procedure?
>
>
>Culling isn't related to the nodes directly, but to a traversersal of
>the scene graph that compares the bounding shere's of internal nodes of
>the scene graph and the bounding boxes of the drawable leaves.  Culling
>can happen at any point in the hierarchy - it can cull right up at the
>top node in the scene graph if the scene is outside the view frustum.
>
>
>Within the cull traversal there is no tracking of culled or non culling
>bounding boxes, a cull test is done and the bool result used directly. 
>There isn't a "bounding box" or "bounding sphere" for culled or non
>culled objects.  All the cull traversal cares about is building a list
>of drawables leaves that pass the view frustum test, there is no
>tracking of any objects that are culled - this would be a crazy waste
>of CPU resources.
>
>
>I have to ask, why do you want a bounding box of culled objects - what
>is the high level problem you are trying to solve?  It may well be that
>you are asking the wrong question thinking about the task you have in
>the wrong way.
>
>
>Robert.
>
>
>thanks for pointing out how cull traversal operates.
>
>Yes, it might be I am searching in the wrong direction. I need to get
>the minimum and the maximum Z coordinate of the geometry vertices in
>order to apply a color range. This is quite easy to do for the whole
>geometry but I would know if there is a way just for the vertices
>inside the view frustum.
>
>Regards,
>Renzo
>
>
>
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>
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